The crank webs of a crankshaft are usually formed to be symmetric with respect to a longitudinal center axis which intersects the axis of rotation of the crankshaft, since the mass balancing of the countershafts must compensate for the rotating and translating parts of the connecting rods, bearings, and journals, and this mass balancing is calculable only when the center of gravity of the masses involved is known. A symmetric crank web is desirable when the centrifugal forces occurring during operation act perfectly symmetrically on an individual crankshaft portion consisting of two webs, two counterweights, two main bearings, and a crankpin.
However, the inventors herein have recognized potential issues with symmetric crank webs. As one example, combustion gas pressure does not act symmetrically on the crank webs, because it usually exerts the greatest force on the piston, connecting rod, and crankpin, only after top dead center. Specifically, the mixture injected into the cylinder combusts with a certain delay, and the highest gas pressure occurs close to the so-called CA50 point, which represents the crankshaft angle of rotation at which approximately 50% of the quantity of injected fuel has been combusted in the cylinder. The CA50 point may lie in a range from approximately 10° to 15°, or even up to 30°, after the top dead center of the piston.
In one example, the issues described above may be at least partially addressed by a crankshaft for a piston internal combustion engine, the crankshaft comprising a crankshaft throw, the crankshaft throw comprising crank webs that are formed asymmetrically in a region of a crankpin with respect to a plane intersecting an axis of rotation of the crankshaft and a center axis of the crankpin, such that the breaking strength of the crankshaft throw is increased at a crankshaft angle of rotation which differs from the top dead center and at which the highest combustion-induced force acts on the crankpin. By constructing the crankshaft webs to be asymmetric, the crankshaft can be subjected to equal or greater loading than a crankshaft of a larger or equal inherent weight having symmetric crankshaft webs.
In another example, a method for producing a crankshaft comprises generating a first crankshaft design which comprises a crankshaft with symmetrically formed crank webs; determining a distribution of loads in the crank webs which occur when a piston driving rotation of the crank webs exerts a maximum force on the crank webs; generating a second crankshaft design based on the first crankshaft design and the distribution of loads in the crank webs, where points of the crank webs which are more loaded at the maximum force are reinforced by the addition of crank web material; and manufacturing the crankshaft based on the second crankshaft design.
As yet another example, a crankshaft for an internal combustion engine comprises a crankpin, and a first crank web coupled to the crankpin, where a center of mass of the crank web is offset from a central axis of the crank web, and where the center of mass is more proximate a leading rotational edge and top of the crank web than a trailing rotational edge and bottom of the crank web.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.